From Beyonce's 'Drunk in Love' song. She pronounces 'surfboard' as 'surfbort' and people take humor from this. It is a Beyonce-ism and sounds funny so has been adopted by the Beyhive as a joke/humorous word. Has been made into t-shirts by various Beyonce fans.

"Then I fill the tub up halfway then ride it with my surfbort
surfbort, surfbort"

Heard most commonly in the Beyonce song "Drunk in Love", Surfbort is a sexual position where a male lays in the tub with his knees bent. The woman straddles him with her back towards him so she can ride his dick by holding onto his thighs, much like holding onto a surfboard and bobbing through the ocean.